As a water removal apparatus, for example, Japanese Patent Laid-open Publication No. 2001-050624 (Reference 1) discloses a cooling apparatus. In such a cooling apparatus, a water removal filter is disposed at a cooling liquid outlet port of a cooling liquid receiving tank provided on a circulation passageway of a cooling liquid so as to send the cooling liquid to a target object after removing water therefrom.
Further, Japanese Patent Laid-open Publication No. 2001-141341 (Reference 2) discloses an air conditioner including a water removal apparatus. In this air conditioner, there is provided, between an outdoor heat exchanger and an expansion valve or a capillary tube, a bypass circuit including a dryer having at its central portion a filter for capturing foreign materials such as dirt, powdered metal or the like during a cooling cycle. The dryer (particularly a molecular sieve) adsorbs and removes water in the coolant passing through the bypass circuit.
Moreover, there has been proposed in Japanese Patent Laid-open Publication No. H05-180538 (Reference 3) a water removal apparatus of a cooling system. In the water removal apparatus, a cooling cylinder for cooling a coolant is disposed on the middle of a bypass passageway for the coolant and a filter for capturing water contained in the coolant is provided at a downstream of the cooling cylinder. After the coolant from the bypass passageway is cooled by the cooling cylinder, the water in the coolant is separated and removed from the coolant.
Furthermore, among the cooling systems, there is a type that cools a target object down to minus several tens of degrees Celsius such as that employed in an inspection apparatus for performing a low temperature inspection for an object to be processed such as a semiconductor wafer. In this case, for example, if a fluorine-based coolant is used and water is dissolved in the coolant, the water is cooled to be frozen on the surface of the heat exchanger of the cooling system and grows to frost or ice, so that the heat transfer efficiency of the heat exchanger and hence the cooling capability of the cooling system are gradually deteriorated. As an approach of solving the above problem, conventionally, after the operation of the cooling system is stopped, the coolant is taken out from the cooling system and the water dissolved in the coolant is removed therefrom by using an external water adsorption filter. Further, the water attached in the heat exchanger and/or the circulation line of the coolant is cleaned out by using, e.g., ethyl alcohol, and a large amount of dry air is blown into the heat exchanger and/or the circulation line to dry the inside thereof.
However, as in the conventional cooling system, if the coolant is taken out from the cooling system to remove the water from the coolant by using the water adsorption filter externally, and additionally or alternatively if the water attached in the heat exchanger and/or the coolant circulation line is cleaned out by using, e.g., the ethyl alcohol and the inside thereof is then dried by using the dry air, the operation efficiency of the cooling system is deteriorated. Further, if the water removal filter is installed on the passageway for the coolant of a low temperature as disclosed in References 1 to 3, the water is frozen to the filter to occlude the latter, which requires the stop of the cooling system.